1. Field of the Invention
The present invention relates to a developing device for developing an electrostatic latent image formed on a charge retaining member in an electrophotographic process, electrostatic printing process, electrostatic recording process and the like.
2. Description of the Prior Art
An electrophotographic copying machine in which an electrophotographic process is utilized is partially schematically illustrated in FIG. 1. In this example, a freely revolvable electrophotosensitive receptor 1 is uniformly charged at first by a charging device 2 as said receptor 1 is revolved, and thereafter an image exposure is carried out by an exposure mechanism 3 to form an electrostatic latent image. Said latent image is developed by a developing device 4 to form a toner image, and the formed toner image is transferred by means of a transfer electrode 5 onto a transfer paper which has been synchronously conveyed on transfer paper passage P to match said toner image, and then the transfer paper is separated from the receptor 1. After the transfer paper is separated therefrom, the receptor 1 is still further revolved to carry out a whole surface exposure to light with an exposing device 6, or the electrostatic charge on the receptor 1 is eliminated by the means of a charge eliminating electrode 7 and then the toner still adhering onto the receptor 1 is removed by a cleaning device 8. The transfer paper onto which the toner image was carried is fixed and then ejected from the copying machine.
In the dry type developing methods for visualizing an electrostatic image in an image-forming process as described above, developer including colored powder (e.g., toner) is used. As to the developer, there have been known a two-component developer comprising a carrier and toner, and a one-component developer consisting of toner, and inter alia, the developing method using the one-component developer is capable of carrying out stable development because the toner density thereof does not relatively change in comparison with those of the methods using the two-component developer, and is advantageous in the simplification of the devices to be used.
Meanwhile, it is required that the toner in the developer should be charged at an opposite polarity to that of an electrostatic latent image on a charge retaining member when said toner is applied to a developing process. In the two-component development system, it is relatively easy to obtain the toner in a satisfactorily charged state because the toner is stirred together with the carrier. However, in the one-component development system, it is very difficult to control the charged polarity and charged volume because there exists no carrier like in the two-component developer, so that it has been a problem awaiting solution in the one-component developer to carry out an excellent development without fail.
Heretofore, as for the improvements on the developing devices using one-component developer, there has been proposed a developing device in which both a first sleeve for supplying a one-component developer onto the charge retaining member for development and a second sleeve for supplying a certain amount of charged one-component developer onto said first sleeve are used so that the charge control of the developer can easily be performed to supply regularly in the developing process or the developing device similar thereto.
On the other hand, as for a cleaning device for removing a residual toner from the charge retaining member, there have been known a blade type, fur brush type and magnetic brush type cleaning device, and the like, and inter alia the magnetic brush type cleaning device which also serves as a developing brush has popularly been known. There is a possibility that one device may commonly serve as a developing and a cleaning device to lower the cost thereof. In such a copying process, the steps of charging, exposing to light, developing, transferring and separating are carried out during the first revolution of the charge retaining member and then a cleaning step is carried out during the second revolution thereof.
In such a combination use, however, it is difficult to satisfy both the development function and the cleaning function, and particularly in the case that the developer to be used is a one-component developer, a development should be carried out so as to be in the state where the developer is brought into soft contact with the charge retaining member in the development area, or so as to work in a non-contact state. The requirement as stated above is also one of the factors causing the difficulties of the combination use stated above.